refilled after every two combustions, it is advisable to keep a little
stock of solution in a bottle fitted with an ordinary cork.
6. A Calcium Chloride U- Tube.—The form of calcium chloride
tube is shown in Fig. 8. It is fitted with sieved calcium
chloride to within 2^ cm. (r in.) of the
side pieces, and then with coarser pieces
to within ^ cm. (£ in.). Place a small
plug of cotton wool in both limbs above
the chloride to keep it in position. Two
well-fitting corks, cut off level with the
glass and coated with sealing-wax, pro-
duce an effective air-tight stopper to the
open limbs, but it is preferable to seal
them in the blow-pipe flame. The sealing requires a little skill.
Carefully wipe off any chloride dust which may have adhered
to the open ends of the two limbs. Cork up one limb and
stopper one of the side tubes. Attach a short piece of rubber
tubing to the other side tube to serve as a mouthpiece. Now
soften the end of the open limb in a small blow-pipe flame, and
at the same time heat the end of a short piece of glass rod.
With the hot end of the rod gather up the edges of the open
limb, and whilst rotating the limb backwards and forwards in
the flame, draw it out and seal it up. If successful, the appear-
ance of the tube is that shown in Fig. 9. The blob of glass is
heated in a small flame, and, by gently blowing and re-heating
and blowing again, the blob can be
removed, and, finally, by using a
rather larger flame, heating and
blowing alternately, the end is
7. A Porcelain or, preferably^ a
Platinum Boat.—See that it slips
easily into the combustion tube.
The boat is kept in a desiccator
on a flat cork or support made of glass rod when not in use.
Preparation of the Tube.—Before starting the com-
bustion it is necessary to clean and dry the combustion tube.
This is effected by heating the whole length of the tube con-
taining the copper oxide and spiral gradually to a dull red heat,
and passing through it a slow stream of dry oxygen from the